U.S. Pat. No. 5,242,194 to Popek discloses an apparatus for inflating an inflatable vehicle occupant restraint such as an air bag. The apparatus includes a container and an actuator assembly. The container defines a cylindrical storage chamber containing gas under pressure, and has a burst disk which closes the storage chamber. A body of pyrotechnic material is contained in the storage chamber with the gas. The actuator assembly includes a piston, a charge of pyrotechnic material, and a squib for igniting the charge of pyrotechnic material.
When the vehicle experiences deceleration of at least a predetermined amount which indicates the occurrence of a vehicle collision, the charge of pyrotechnic material in the actuator assembly is ignited by the squib. The charge of pyrotechnic material then generates combustion products which propel the piston forcefully against the burst disk to rupture the burst disk. The gas in the storage chamber is thus released to exit the storage chamber through an opening defined by the ruptured burst disk. A diffuser then directs the gas into the air bag to inflate the air bag.
Additionally, the combustion products generated by the charge of pyrotechnic material are directed into the storage chamber through a passage extending through the piston. The combustion products are thus directed against the body of pyrotechnic material in the storage chamber to ignite the body of pyrotechnic material. When the body of pyrotechnic material burns in the storage chamber, it generates additional combustion products which increase the gas pressure in the storage chamber by heating the stored gas and by generating additional gas. As a result, the apparatus provides gas for inflating the air bag at an elevated pressure level which is greater than the pressure level at which the gas is originally contained in the storage chamber.
A similar apparatus for inflating an inflatable vehicle occupant restraint is disclosed in co-pending U.S. patent application Ser. No. 135,786, filed Oct. 13, 1993, entitled "A Vehicle Occupant Restraint Inflator," and assigned to TRW Vehicle Safety Systems Inc. In that apparatus, the storage chamber contains a mixture of gases. The mixture of gases includes a primary gas for inflating the vehicle occupant restraint, and further includes a combustible gas. The apparatus also includes a charge of pyrotechnic material for generating combustion products that propel a piston forcefully against a burst disk which closes the storage chamber. The piston then ruptures the burst disk to open the storage chamber, and also directs the combustion products from the charge of pyrotechnic material into the mixture of gases in the storage chamber. The combustible gas in the mixture of gasses is thus ignited and, as a result, the mixture of gases is heated and pressurized.